1. Field of the Invention
The present invention relates generally to a sputtering device, and more particularly to an integrated device for forming multi-layer thin film structures on a substrate, and to a method for depositing at least one layer of film on a substrate using such a device.
2. Description of Related Art
Coating of a substrate by sputtering is a well established art. Deposition by sputtering is generally performed as follows: Atoms of an inert gas such as Argon (Ar) are ionized into positive ions by a glow discharge. These positive ions are accelerated toward a cathode or target by an electric field and then impinged upon the target. As a result of the ionic bombardment, neutral atoms and ions are transferred from the target surface into a vacuum chamber due to the exchange of momentum there between. The liberated or sputtered atoms and ions are consequently deposited on a pre-selected substrate disposed in the vacuum chamber.
In planar-magnetron-sputtering, the cathode includes an array of permanent magnets arranged in a closed loop and mounted in a fixed position in relation to a flat target plate. Thus, the magnetic field is caused to travel in a closed loop, commonly referred to as a xe2x80x9crace track,xe2x80x9d which establishes the path or region along which sputtering of the target material takes place. In the magnetron cathode, a magnetron field confines the glow discharge plasma and increases the path length of the electrons moving under the influence of the electric field. This results in an increase in the gas atom-electron collision probability and leads to a much higher sputtering rate than that obtained without the use of magnetic confinement. Further, the sputtering process can be accomplished at a much lower gas pressure.
In facing-targets-sputtering, the cathode consists of two opposing magnetron targets. Electrons are emitted from both target plates by applying voltage thereto. These electrons are confined between the target plates due to a magnetic field which promotes the ionization of the inert gas, thereby forming a plasma region. The positive ions of the inert gas excited in the plasma region are accelerated toward the target plates, whereby those accelerated particles violently impinge upon the target plates. The bombardment of the target plates by accelerated particles of the inert gas and ions thereof causes an emission of atoms from the material forming the plates. The substrate on which the film is to be disposed is placed around the plasma region, so that the bombardment of electrons and high energy negative ion particles, such as negative oxygen ions, against the thin film plane is avoided due to effective confinement of the plasma region by the magnetic field. This results in a decreased roughness of film surface and only a relatively small rise in substrate temperature. Furthermore, films with different composition can be prepared without the need to exchange targets by providing target plates made of different materials connected to independent power supplies. Facing-targets-sputtering has a lower sputtering rate than that of planar-magnetron-sputtering, because the former has a weaker magnetic field component parallel to the target surface than does the latter.
In multi-layer thin film structures, the deposition requirements of each layer may differ. For example, some of the layers may be required to be very thin and smooth, whereas other layers may require a specific rate of deposition.
It is an aim of the present invention, therefore, to provide a sputtering device for producing on a substrate, multi-layer film structures, of which a wide range of deposition requirements for each individual layer can be met.
According to a first aspect of the present invention, there is provided a sputtering device for depositing multi-layer films on a substrate, the sputtering device comprising at least one planar-magnetron-sputtering-cathode and at least one facing-targets-sputtering-cathode housed in a single vacuum chamber, and adapted such that each of the planar-magnetron-sputtering-cathode and each of the facing-targets-sputtering-cathode can be selectively positioned for sputtering deposition onto a substrate.
The combination of planar-magnetron-sputtering-cathodes and facing-targets-sputtering-cathodes in a single device has the advantage that a wide range of deposition requirements can be met. Each planar-magnetron-sputtering-cathode and each facing-targets-sputtering-cathode are preferably mounted for rotation about a common axis between a working position in which the respective cathode is used to deposit a layer on a substrate, and a non-working position in which the respective cathode is not used to deposit a layer on said substrate. Preferably, electrical connections to the planar-magnetron-sputtering-cathode and the pair of facing-targets-sputtering-cathode are shielded to atmospherically isolate them from the single vacuum chamber.
Moreover, cooling of the planar-magnetron-sputtering-cathode and the pair of facing-targets-sputtering-cathode is accomplished using a coolant fluid supplied via supply means. The cooling mechanisms are also preferably shielded to atmospherically isolate them from the single vacuum chamber.
According to a preferred embodiment, the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode can be positioned for sputtering deposition onto a substrate in an arbitrary sequence, and the device is adapted such that a substrate can be spun during deposition of a layer thereon. The device is preferably further adapted such that the distance between the surface of a substrate to be subject to deposition and the planar-magnetron-sputtering-cathode and/or the facing-targets-sputtering-cathode can be varied. The device is also preferably adapted such that the distance between the two facing targets of the facing-targets-sputtering-cathode can be varied. In a preferred embodiment, the two facing targets are mounted for movement along a common rail such that the distance between them can be varied.
The sputtering device further preferably comprises one or more of the following components: a load-lock component which can accommodate a plurality of substrates; an in situ measuring instrument having an incident source and a detecting source which are arranged to be in a common plane with a substrate during sputtering deposition onto said substrate; and an assisted ion source, electron source, or light source for assisting the deposition by the planar-magnetron-sputtering-cathode or the facing-targets-sputtering-cathode.
According to a second aspect of the present invention, there is provided a method for depositing a film on a substrate using the device described above wherein the substrate is spun whilst rotating the planar-magnetron-sputtering-cathode or the facing-targets-sputtering-cathode over the substrate through the working position for sputtering deposition onto the substrate.
According to a third aspect of the present invention, there is provided a sputtering device for depositing multi-layer films on a substrate, the sputtering device comprising a first vacuum chamber, at least one planar-magnetron-sputtering-cathode and at least one facing-targets-sputtering-cathode for sputtering deposition onto a substrate in the first vacuum chamber. The sputtering device is adapted such that a substrate can be moved within the first vacuum chamber between a position for deposition thereon using the planar-magnetron-sputtering-cathode and a position for deposition thereon using the facing-targets-sputtering-cathode, and further adapted such that the planar-magnetron-sputtering-cathode or the pair of facing-targets-sputtering-cathode can be atmospherically isolated from each other and from the first vacuum chamber.
The sputtering device is preferably adapted such that the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode can be positioned for sputtering deposition onto the substrate in an arbitrary sequence, and/or such that at least one of the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode can be exchanged for another cathode.
The sputtering device preferably further comprises a heating station, and is adapted such that a substrate can be moved to a position within the first vacuum chamber where it may be subject to heating using the heating station.
According to a preferred embodiment, the device is adapted such that a substrate can be positioned at a range of distances from the planar-magnetron-sputtering-cathode and/or the facing-targets-sputtering-cathode. The device is preferably further adapted such that the distance between the two facing targets of the facing-targets-sputtering-cathode can be changed. This can be achieved by mounting the two facing targets for movement along a common rail.
In a preferred embodiment, the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode are positioned such that a substrate can be moved into a position in which simultaneous sputtering deposition can be carried out with respect to two opposite sides of the substrate. In one embodiment, the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode are provided in an open in-line configuration, i.e. they are positioned such that a substrate can be moved between the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode by moving the substrate in a linear fashion. In an alternative embodiment, the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode are provided in a closed in-line configuration, i.e. they are positioned such that a substrate can be moved between the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode by movement around a continuous path.
The device preferably includes a substrate holder that is mounted for movement between the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode, and that is adapted for holding a substrate such that the substrate can be spun on the substrate holder. In a preferred embodiment, the substrate holder is mounted for rotation between the planar-magnetron-sputtering-cathode and the facing-targets-sputtering-cathode. The deposition is carried out whilst moving (by rotation, for example) the substrate holder through a position in which the substrate faces the working cathode, and spinning the substrate on the substrate holder. This method of deposition is a fourth aspect of the present invention.
The sputtering device according to the third aspect of the present invention preferably comprises a plurality of planar magneton sputtering cathodes and/or a plurality of facing-targets-sputtering-cathodes, and is adapted such that two or more of the plurality of planar-magnetron-sputtering-cathodes and/or two or more facing-targets-sputtering-cathodes can be atmospherically isolated together from the first vacuum chamber.